Fin tube heat exchanger

ABSTRACT

A fin tube heat exchanger has heat transfer fins disposed in an air flow and plural heat transfer tubes that are inserted in the heat transfer fins and disposed in a direction substantially orthogonal to a flow direction of the air flow. On the heat transfer fins, a set of guide fins and a set of guide fins arranged straightly from upstream to downstream in the flow direction of the air flow are formed, by cutting and raising, on the heat transfer fin surfaces on both sides of the heat transfer tubes. Straight lines that hypothetically interconnect the guide fins and the guide fins slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes to rear sides of the heat transfer tubes in the flow direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fin tube heat exchanger, and in particular to a fin tube heat exchanger having heat transfer fins disposed in an air flow and plural heat transfer tubes that are inserted in the heat transfer fins and disposed in a direction substantially orthogonal to a flow direction of the air flow.

2. Background Information

Conventionally, fin tube heat exchangers (i.e., cross fin and tube heat exchangers) having heat transfer fins disposed in an air flow and plural heat transfer tubes that are inserted in the heat transfer fins and disposed in a direction substantially orthogonal to a flow direction of the air flow have been widely used in air conditioners and the like.

In such fin tube heat exchangers, as a heat transfer promoting technique for the purpose of reducing dead water regions formed in the portions of the heat transfer tubes in the heat transfer fins downstream in the flow direction of the air flow and for the purpose of renewing the boundary layers in the heat transfer fins, a technique of forming, by cutting and raising and in positions on the heat transfer fin surfaces on both sides of the heat transfer tubes, guide fins that become larger and open upstream in the flow direction of the air flow has been employed (see Japanese Patent Application Publication (JP-A) No. 61-110889).

SUMMARY OF THE INVENTION

However, when a fin tube heat exchanger in which the aforementioned guide fins are employed is used as an evaporator of a heat medium such as refrigerant which uses air as a heat source such as represented by air conditioners and the like, a problem arises in that drain water occurring due to heat exchange between the air and the heat medium accumulates on the guide fins and increases ventilation resistance. Further, when a fin tube heat exchanger in which the aforementioned guide fins are employed is used as an outdoor heat exchanger configuring an outdoor unit of an air conditioner, a problem arises in that, although sometimes frost occurring on the heat transfer fin surfaces is removed by defrosting operation, water drainability is lowered in this case.

It is an object of the present invention to simultaneously achieve a heat transfer promoting effect and water drainability by guide fins in a fin tube heat exchanger.

A fin tube heat exchanger pertaining to a first invention comprises: heat transfer fins disposed in an air flow; and plural heat transfer tubes that are inserted in the heat transfer fins and disposed in a direction substantially orthogonal to a flow direction of the air flow. On the heat transfer fins, plural guide fins arranged straightly from upstream to downstream in the flow direction of the air flow are formed, by cutting and raising, on the heat transfer fin surfaces on both sides of the heat transfer tubes. Straight lines that hypothetically interconnect the plural guide fins slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes to rear sides of the heat transfer tubes in the flow direction of the air flow.

In this fin tube heat exchanger, the guide fins are plurally divided from upstream to downstream in the flow direction of the air flow, and the plural guide fins slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes to rear sides of the heat transfer tubes in the flow direction of the air flow, so mainly the effect of renewing the boundary layers can be reliably obtained by the guide fins of the plural guide fins that are disposed on the front sides of the heat transfer fins in the flow direction of the air flow and the effect of reducing dead water regions formed of the rear sides of the heat transfer fins in the flow direction of the air flow can be obtained by the guide fins that are disposed on the rear sides of the heat transfer fins in the flow direction of the air flow, and it can be made easier for drain water occurring on the heat transfer fin surfaces to be drained from gaps between the guide fins. Thus, a heat transfer promoting effect by the guide fins can be obtained without being affected by drain water occurring on the heat transfer fin surfaces.

Moreover, because the plural guide fins are straightly arranged from upstream to downstream in the flow direction of the air flow, the guide fins of the plural guide fins that are disposed on the rear sides of the heat transfer fins in the flow direction of the air flow have the same inclination as the guide fins that are disposed on the front sides in the flow direction of the air flow, so not only do they reduce dead water regions formed in portions on the rear sides of the heat transfer tubes in the flow direction of the air flow, but they can prevent new dead water regions from being formed on the backs of the guide fins.

As described above, in the fin tube heat exchanger pertaining to the present invention, the effect of promoting heat transfer by the guide fins can be obtained without being affected by drain water occurring on the heat transfer fin surfaces, and new dead water regions can be prevented from being formed on the backs of the guide fins, so a heat transfer promoting effect and water drainability by the guide fins can be simultaneously achieved.

A fin tube heat exchanger pertaining to a second invention is the fin tube heat exchanger pertaining to the first invention, wherein the height of each of the guide fins gradually increases downstream in the flow direction of the air flow.

In this fin tube heat exchanger, by giving each of the guide fins a shape whose height gradually increases downstream in the flow direction of the air flow, vertical vortexes can be created on the back of each of the guide fins, so that the heat transfer promoting effect by the guide fins can be further raised.

A fin tube heat exchanger pertaining to a third invention is the fin tube heat exchanger pertaining to the first or second invention, wherein a water drainage promoting portion for causing water accumulating between the guide fins that are mutually adjacent on the straight lines to flow downward is formed in the heat transfer fins.

In this fin tube heat exchanger, the water drainage promoting portion is formed between the guide fins, so the ability of the guide fins to drain water can be further raised.

A fin tube heat exchanger pertaining to a fourth invention is the tin tube heat exchanger pertaining to the third invention, wherein the water drainage promoting portion is a slit formed between the guide fins that are mutually adjacent on the straight lines.

A fin tube heat exchanger pertaining to a fifth invention is the fin tube heat exchanger pertaining to the third invention, wherein the water drainage promoting portion is a cutout formed in end portions of the guide fins that are mutually adjacent on the straight lines, which end portions are portions that become lower end portions of the guide fins.

A fin tube heat exchanger pertaining to a sixth invention is the fin tube heat exchanger pertaining to the third invention, wherein the water drainage promoting portion is a water-conducting rib formed between the guide fins that are mutually adjacent on the straight lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a fin tube heat exchanger pertaining to a first embodiment of the present invention.

FIG. 2 is a cross-sectional diagram along A-A of FIG. 1.

FIG. 3 is a cross-sectional diagram along B-B of FIG. 1.

FIG. 4 is a diagram showing a fin tube heat exchanger pertaining to a modification of the first embodiment, the diagram showing portion C of FIG. 1.

FIG. 5 is a diagram showing a fin tube heat exchanger pertaining to a modification of the first embodiment, the diagram showing portion C of FIG. 1.

FIG. 6 is a diagram showing a fin tube heat exchanger pertaining to a modification of the first embodiment, the diagram showing portion C of FIG. 1.

FIG. 7 is a cross-sectional diagram of a fin tube heat exchanger pertaining to a second embodiment of the present invention.

FIG. 8 is a cross-sectional diagram along A-A of FIG. 7.

FIG. 9 is a cross-sectional diagram along B-B of FIG. 7.

FIG. 10 is a diagram showing a fin tube heat exchanger pertaining to a modification of the second embodiment, the diagram showing portion C of FIG. 7.

FIG. 11 is a diagram showing a fin tube heat exchanger pertaining to a modification of the second embodiment, the diagram showing portion C of FIG. 7.

FIG. 12 is a diagram showing a fin tube heat exchanger pertaining to a modification of the second embodiment, the diagram showing portion C of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Below, embodiments of a fin tube heat exchanger pertaining to the present invention will be described on the basis of the drawings.

First Embodiment

In FIG. 1 to FIG. 3, there are shown relevant portions of a fin tube heat exchanger 1 pertaining to a first embodiment of the present invention. Here, FIG. 1 is a cross-sectional diagram of the fin tube heat exchanger 1. FIG. 2 is a cross-sectional diagram along A-A of FIG. 1. FIG. 3 is a cross-sectional diagram along B-B of FIG. 1.

Basic Configuration of Fin Tube Heat Exchanger

The fin tube heat exchanger 1 is a cross fin and tube heat exchanger and is mainly disposed with plural plate-shaped heat transfer fins 2 and plural heat transfer tubes 3. The heat transfer fins 2 are disposed so as to be arranged in a plate thickness direction in a state where the planar direction thereof is generally along a flow direction of an air flow such as that of air. Plural through holes 2 a are formed in the heat transfer fins 2 at intervals in a direction substantially orthogonal to the flow direction of the air flow. Portions around the through holes 2 a serve as annular collar portions 23 that project towards one side in the plate thickness direction of the heat transfer fins 2. The collar portions 23 contact surfaces of the heat transfer fins 2 adjacent in the plate thickness direction that are opposite of surfaces where the collar portions 23 are formed, such that a predetermined interval H is ensured between each of the heat transfer fins 2 in the plate thickness direction. The heat transfer tubes 3 are tube members inside of which a heat medium such as refrigerant flows; the heat transfer tubes 3 are inserted in the plural heat transfer fins 2, which are disposed so as to be arranged in the plate thickness direction, and disposed in a direction substantially orthogonal to the flow direction of the air flow. Specifically, the heat transfer tubes 3 penetrate the through holes 2 a formed in the heat transfer fins 2 and tightly contact the inner surfaces of the collar portions 23 as a result of tube expansion work during assembly of the fin tube heat exchanger 1.

Further, the fin tube heat exchanger 1 of the present embodiment is used in a state where the arranging direction of the plural heat transfer tubes 3 is in a substantially vertical direction. For this reason, the air flow flows so as to cross through the fin tube heat exchanger 1 in a substantially horizontal direction. It will be noted that in the following description, when language such as “upper side” or “upward” and “lower side” or “downward” is used, this will indicate the arranging direction of the heat transfer tubes 3.

(2) Detailed Shape of Heat Transfer Fins

Next, the detailed shape of the heat transfer fins 2 used in the fin tube heat exchanger 1 of the present embodiment will be described.

On the heat transfer fins 2, plural (in the present embodiment, two) a set of guide fins 21 a and 21 b and a set of guide fins 21 c and 21 d arranged straightly from upstream to downstream in the flow direction of the air flow are formed, by cutting and raising, on the heat transfer fin 2 surfaces on both sides of each of the heat transfer fins 3 (i.e., the lower side and the upper side of each of the heat transfer fins 3). Straight lines L₁ and L₂ that hypothetically interconnect the guide fins 21 a and 21 b and the guide fins 21 c and 21 d slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes 3 to rear sides of the heat transfer tubes 3 in the flow direction of the air flow. Here, attack angles α₁ and α₂ that the straight lines L₁ and L₂ form with respect to the flow direction of the air flow are set to be within the range of 10° to 30°.

Further, each of the guide fins 21 a to 21 d is formed such that its height gradually increases downstream in the flow direction of the air flow. In the present embodiment, each of the guide fins 21 a to 21 d is substantially trapezoidal or substantially triangular (see FIG. 3; FIG. 3 is a diagram showing the guide fins 21 c and 21 d, but the guide fins 21 a and 21 b also have the same shape) and is formed such that its maximum height h is less than the height H of the collar portions 23. Further, slit holes 22 a to 22 d that are formed in the heat transfer fins 2 when the guide fins 21 a to 21 d are cut and raised are disposed on the far sides of the heat transfer fins 3 with the guide fins 21 a to 21 d being interposed therebetween.

(3) Characteristics of Fin Tube Heat Exchanger

In the fin tube heat exchanger 1 configured as described above, the guide fins formed on both sides of each of the heat transfer tubes 3 are divided into the plural (in the present embodiment, two) the set of the guide fins 21 a and 21 b and the set of the guide fins 21 c and 21 d from upstream to downstream in the flow direction of the air flow, and the set of the guide fins 21 a and 21 b and the set of the guide fins 21 c and 21 d slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes 3 to the rear sides of the heat transfer tubes 3 in the flow direction of the air flow, so mainly the effect of renewing the boundary layers can be reliably obtained by the guide fins 21 a and 21 c of the guide fins 21 a to 21 d that are disposed on the front sides of the heat transfer fins 2 in the flow direction of the air flow and the effect of reducing dead water regions formed on portions of the rear sides of the heat transfer fins 3 in the flow direction of the air flow can be obtained by the guide fins 21 b and 21 d that are disposed on the rear sides of the heat transfer fins 2 in the flow direction of the air flow, and it can be made easier for drain water occurring on the heat transfer fin 2 surfaces to be drained from between the guide fins 21 a and 21 b and between the guide fins 21 c and 21 d. Thus, a heat transfer promoting effect by the guide fins 21 a to 21 d can be obtained without being affected by drain water occurring on the heat transfer fin 2 surfaces.

Moreover, because the guide fins 21 a and 21 b and the guide fins 21 c and 21 d are straightly arranged on the straight lines L₁ and L₂ from upstream to downstream in the flow direction of the air flow, the guide fins 21 b and 21 d of the guide fins 21 a to 21 d that are disposed on the rear sides of the heat transfer fins 2 in the flow direction of the air flow have the same inclination as the guide fins 21 a and 21 c that are disposed on the front sides in the flow direction of the air flow, so not only do they reduce dead water regions formed in portions on the rear sides of the heat transfer tubes 3 in the flow direction of the air flow, but they can prevent new dead water regions from being formed on the backs of the guide fins 21 b and 21 d.

As described above, in the fin tube heat exchanger 1 of the present embodiment, a heat transfer promoting effect by the guide fins 21 a to 21 d can be obtained without being affected by drain water occurring on the heat transfer fin 2 surfaces, and new dead water regions can be prevented from being formed on the backs of the guide fins 21 b and 21 d, so a heat transfer promoting effect and water drainability by the guide fins can be simultaneously achieved.

Further, in this fin tube heat exchanger 1, by giving each of the guide fins 21 a to 21 d a shape whose height gradually increases downstream in the flow direction of the air flow, vertical vortexes can be formed on the back of each of the guide fins 21 a to 21 d, so the heat transfer promoting effect by each of the guide fins 21 a to 21 d can be further raised.

(4) Modifications

In the aforementioned fin tube heat exchanger 1, slits 32 and 35 (see FIG. 4), cutouts 42 and 43 (see FIG. 5), or a water-conducting rib 52 (see FIG. 6) serving as a water drainage promoting portion to cause water accumulating between the guide fins 21 a and 21 b and the guide fins 21 c and 21 d that are mutually adjacent on the straight lines L₁ and L₂ to flow downward may be formed in order to make it easier for drain water occurring on the heat transfer fin 2 surfaces to be drained from gaps between the guide fins 21 a and 21 b and between the guide fins 21 c and 21 d. Here, FIG. 4 to FIG. 6 are diagrams showing portion C of FIG. 1 when each type of water drainage promoting portion is formed in the heat transfer fins 2.

First, a case where the slits 32 and 35 are formed in the heat transfer fins 2 will be described using FIG. 4. In the present modification, the slits 32 and 35 are formed, so as to cross the straight lines L₁ and L₂ in the vertical direction, in gap portions between the guide fins 21 a and 21 b that are mutually adjacent on the straight line L₁ and between the guide fins 21 c and 21 d that are mutually adjacent on the straight line L₂. Here, the slits 32 and 35 are given a narrow slit width by forming vertical incisions in the heat transfer fins 2, for example, in order to ensure that the slits 32 and 35 do not, as much as possible, affect heat transfer performance. Further, slits 31, 33, 34 and 36 that are the same as the slits 32 and 35 may also be formed in the end portions of the guide fins 21 a to 21 d other than the gap portions between the guide fins 21 a and 21 b and between the guide fins 21 c and 21 d.

Next, a case where the cutouts 42 and 43 are formed in the heat transfer fins 2 will be described using FIG. 5. In the present modification, the cutouts 42 and 43 are formed in end portions of the guide fins 21 a and 21 b and the guide fins 21 c and 21 d that are mutually adjacent on the straight lines L₁ and L₂, which end portions become lower end portions of the guide fins 21 a and 21 b and the guide fins 21 c and 21 d (i.e., portions that become lower portions of the guide fins 21 a and 21 b and the guide fins 21 c and 21 d along the direction of gravitational force). Specifically, the cutouts 42 and 43 are formed in the lower end portion of the guide fin 21 b and in the lower end portion of the guide fin 21 c. Here, the cutouts 42 and 43 are vertical incisions formed in the lower end portions of the guide fins 21 b and 21 c so as to be communicated with the slits 22 b and 22 c that are formed when forming the guide fins 21 c and 21 c by cutting and raising. Further, cutouts 41 and 44 that are the same as the cutouts 42 and 43 may also be formed in the end portions of the guide fins 21 a and 21 d other than the portions that become the lower end portions of the guide fins 21 b and 21 c.

Next, a case where the water-conducting rib 52 is formed on the heat transfer fins 2 will be described using FIG. 6. In the present modification, the water-conducting rib 52 is formed, so as to cross the straight lines L₁ and L₂ in the vertical direction, in gap portions between the guide fins 21 a and 21 b that are mutually adjacent on the straight line L₁ and between the guide fins 21 c and 21 d that are mutually adjacent on the straight line L₂. Here, the water-conducting rib 52 is a long and narrow projection that extends upward and is formed by pressing the heat transfer fin 2 surfaces, and the water-conducting rib 52 is formed so as to continuously interconnect, in the vertical direction (i.e., in the direction of gravitational force), the gap portion between the guide fins 21 a and 21 b and the gap portion between the guide fins 21 c and 21 d. It will be noted that in the vicinities of the heat transfer tubes 3, the water-conducting rib 52 cannot be straightly extended in the vertical direction, so by forming just the portion thereof in the vicinity of the collar portion 23 in a circular arc shape, a state where the water-conducting rib 52 is continuously formed in substantially the direction of gravitational force can be maintained. Further, water-conducting ribs 51 and 53 that are the same as the water-conducting rib 52 may also be formed on the portion on the front side of the guide fins 21 a and 21 c in the flow direction of the air flow and the portion on the rear side of the guide fins 21 b and 21 d in the flow direction of the air flow other than the gap portion between the guide fins 21 a and 21 b and the gap portion between the guide fins 21 c and 21 d.

As described above, in the fin tube heat exchanger 1 of the present modification, the ability of the heat transfer fins 2 to drain water can be further raised because the slits 32 and 35, the cutouts 42 and 43, or the water-conducting rib 52 serving as a water drainage promoting portion are formed between the guide fins 21 a and 21 b that are mutually adjacent on the straight line L₁ of the heat transfer fins 2 and between the guide fins 21 c and 21 d that are mutually adjacent on the straight line L₂.

Second Embodiment

In FIG. 7 to FIG. 9, there are shown relevant portions of a fin tube heat exchanger 101 pertaining to a second embodiment of the present invention. Here, FIG. 7 is a cross-sectional diagram of the fin tube heat exchanger 101. FIG. 8 is a cross-sectional diagram along A-A of FIG. 7. FIG. 9 is a cross-sectional diagram along B-B of FIG. 7.

Configuration of Fin Tube Heat Exchanger

The basic configuration of the fin tube heat exchanger 101 is the same as the configuration of the fin tube heat exchanger 1 of the first embodiment except for guide fins 121 a to 121 f of later-described heat transfer fins 102. For this reason, description in regard to the basic configuration of the fin tube heat exchanger 101 will be omitted by changing the reference numerals that relate to the heat transfer fins 102 from the 10s to the 100s.

Next, the detailed shape of the heat transfer fins 102 used in the fin tube heat exchanger 101 of the present embodiment will be described.

On the heat transfer fins 102, plural (in the present embodiment, three) a set of guide fins 121 a, 121 b and 121 c and a set of guide fins 121 d, 121 e and 121 f arranged straightly from upstream to downstream in the flow direction of the air flow are formed, by cutting and raising, on the heat transfer fin 2 surfaces on both sides of each of the heat transfer fins 3 (i.e., the lower side and the upper side of each of the heat transfer fins 3). Straight lines L₁ and L₂ that hypothetically interconnect the guide fins 121 a, 121 b and 121 c and the guide fins 121 d, 121 e and 121 f slant with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes 3 to the rear sides of the heat transfer tubes 3 in the flow direction of the air flow. Here, attack angles α₁ and α₂ that the straight lines L₁ and L₂ form with respect to the flow direction of the air flow are set to be within the range of 10° to 30°.

Further, each of the guide fins 121 a to 121 f is formed such that its height gradually increases downstream in the flow direction of the air flow. In the present embodiment, each of the guide fins 121 a to 121 f is substantially trapezoidal or substantially triangular (see FIG. 9; FIG. 9 is a diagram showing the guide fins 121 d, 121 e and 121 f, but the guide fins 121 a, 121 b and 121 c also have the same shape) and is formed such that its maximum height h is less than the height H of collar portions 123. Further, slit holes 122 a to 122 f that are formed in the heat transfer fins 102 when the guide fins 121 a to 121 f are cut and raised are disposed on the far sides of the heat transfer fins 3 with the guide fins 121 a to 121 f being interposed therebetween.

As described above, in the fin tube heat exchanger 101 of the present embodiment configured as described above, whereas the guide fins of the fin tube heat exchanger 1 of the first embodiment had a two-division structure comprising the set of the guide fins 21 a and 21 b and the set of the guide fins 21 c and 21 d, the guide fins here have a three-division structure comprising the set of the guide fins 121 a, 121 b and 121 c and the set of the guide fins 121 d, 121 e and 121 f, so the number of gaps between the guide fins for draining drain water occurring on the heat transfer fin 102 surfaces increases. For this reason, the ability to drain water can be raised in comparison to the fin tube heat exchanger 1 of the first embodiment.

(2) Modifications

In the aforementioned fin tube heat exchanger 101 also, similar to the fin tube heat exchanger 1 of the first embodiment, slits 132, 133, 136 and 137 (see FIG. 10), cutouts 142, 143, 144 and 145 (see FIG. 11), or water-conducting ribs 152 and 153 (see FIG. 12) serving as a water drainage promoting portion that causes water accumulating between the guide fins 121 a and 121 b, between the guide fins 121 b and 121 c, between the guide fins 121 d and 121 e, and between the guide fins 121 e and 121 f that are mutually adjacent on the straight lines L₁ and L₂ to flow downward may be formed in order to make it easier for drain water occurring on the heat transfer fin 102 surfaces to be drained from gaps between the guide fins 121 a and 121 b, between the guide fins 121 b and 121 c, between the guide fins 121 d and 121 e, and between the guide fins 121 e and 121 f. Here, FIG. 10 to FIG. 12 are diagrams showing portion C of FIG. 7 when each type of water drainage promoting portion is formed in the heat transfer fins 102.

It will be noted that, because the shapes and the like of the slits, the cutouts and the water-conducting ribs are the same as those of the slits 32 and 35, the cutouts 42 and 43, and the water-conducting ribs 52 pertaining to the modifications of the first embodiment, description thereof will be omitted. Further, in this fin tube heat exchanger 101 also, similar to the fin tube heat exchanger 1 pertaining to the modifications of the first embodiment, slits 131, 134, 135 and 138, cutouts 141 and 146, or water-conducting ribs 151 and 154 may also be formed in portions other than between the guide fins 121 a and 121 b, between the guide fins 121 b and 121 c, between the guide fins 121 d and 121 e, and between the guide fins 121 e and 121 f.

Other Embodiments

Embodiments of the present invention have been described above on the basis of the drawings, but the specific configurations thereof are not limited to these embodiments and are alterable in a range that does not depart from the gist of the invention.

INDUSTRIAL APPLICABILITY

By utilizing the present invention, a heat transfer promoting effect and water drainability by guide tins can be simultaneously achieved in a fin tube heat exchanger. 

1. A fin tube heat exchanger comprising: heat transfer fins disposed in an air flow; and plural heat transfer tubes inserted in the heat transfer fins and disposed in a direction substantially orthogonal to a flow direction of the air flow, wherein the heat transfer fins include a plurality of guide fins arranged straight from upstream to downstream in the flow direction of the air flow formed by cutting and raising on the heat transfer fin surfaces on both sides of the heat transfer tubes, and straight lines that hypothetically interconnect the guide fins are inclined with respect to the flow direction of the air flow so as to guide the air flow in the vicinities of the heat transfer tubes to rear sides of the heat transfer tubes in the flow direction of the air flow.
 2. The fin tube heat exchanger of claim 1, wherein the height of each of the guide fins gradually increases downstream in the flow direction of the air flow.
 3. The fin tube heat exchanger of claim 1, wherein the heat transfer fins include a water drainage promoting portion for causing water accumulating between the guide fins to flow downward.
 4. The fin tube heat exchanger of claim 3, wherein the water drainage promoting portion is a slit formed between adjacent ones of the guide fins.
 5. The fin tube heat exchanger of claim 3, wherein the water drainage promoting portion is a cutout formed in end portions of mutually adjacent ones of the guide fins.
 6. The fin tube heat exchanger of claim 3, wherein the water drainage promoting portion is a water-conducting rib formed between adjacent ones of the guide fins. 